Intelligent reflecting surface (IRS) is a new and revolutionizing technology for achieving spectrum and energy efficient wireless networks. By leveraging massive low-cost passive elements that are able to reflect radio-frequency (RF) signals with adjustable phase shifts, IRS can achieve high passive beamforming gains, which are particularly appealing for improving the efficiency of RF-based wireless power transfer. Motivated by the above, we study in this paper an IRS-assisted simultaneous wireless information and power transfer (SWIPT) system. Specifically, a set of IRSs are deployed to assist in the information/power transfer from a multi-antenna access point (AP) to multiple single-antenna information users (IUs) and energy users (EUs), respectively. We aim to minimize the transmit power at the AP via jointly optimizing its transmit precoders and the reflect phase shifts at all IRSs, subject to the quality-of-service (QoS) constraints at all users, namely, the individual signal-to-interference-plus-noise ratio (SINR) constraints at IUs and the energy harvesting constraints at EUs. However, this optimization problem is non-convex with intricately coupled variables, for which the existing alternating optimization approach is shown to be inefficient as the number of QoS constraints increases. To tackle this challenge, we first apply proper transformations on the QoS constraints and then propose an efficient iterative algorithm by applying the penalty-based optimization method. Moreover, by exploiting the short-range coverage of IRS, we further propose a more computationally efficient algorithm by optimizing the phase shifts at all IRSs in parallel. Simulation results demonstrate the effectiveness of employing multiple IRSs for enhancing the performance of SWIPT systems as well as the significant performance gains achieved by our proposed algorithms over benchmark schemes. The impact of IRS on the transmitter/receiver design for SWIPT is also unveiled.

中文翻译：

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QoS约束下智能反射面辅助SWIPT的联合主动和被动波束成形优化

智能反射面 (IRS) 是一种全新的革命性技术，用于实现频谱和节能无线网络。通过利用能够反射具有可调相移的射频 (RF) 信号的大量低成本无源元件，IRS 可以实现高无源波束成形增益，这对于提高基于 RF 的无线电力传输的效率特别有吸引力。受上述启发，我们在本文中研究了 IRS 辅助的同步无线信息和电力传输 (SWIPT) 系统。具体而言，部署了一组 IRS 来帮助从多天线接入点 (AP) 分别向多个单天线信息用户 (IU) 和能源用户 (EU) 传输信息/功率。我们的目标是通过联合优化其发射预编码器和所有 IRS 的反射相移来最小化 AP 的发射功率，受所有用户的服务质量 (QoS) 约束，即单个信号干扰IU 的加噪声比 (SINR) 约束和 EU 的能量收集约束。然而，这个优化问题是非凸的，具有错综复杂的耦合变量，随着 QoS 约束数量的增加，现有的交替优化方法被证明效率低下。为了应对这一挑战，我们首先对 QoS 约束应用适当的转换，然后通过应用基于惩罚的优化方法提出一种有效的迭代算法。此外，通过利用 IRS 的短程覆盖，我们通过并行优化所有 IRS 的相移，进一步提出了一种计算效率更高的算法。仿真结果证明了采用多个 IRS 来提高 SWIPT 系统性能的有效性，以及我们提出的算法在基准方案上实现的显着性能提升。还公布了 IRS 对 SWIPT 发射器/接收器设计的影响。